Useful UV light for disinfecting air, water, and surfaces is generally considered to be in the range between 400 nm and 100 nm. Such UV may break down molecular bonds within DNA, which kills or inactivates microorganisms. The specific bands of UV wavelengths for effectively killing various types of organisms have been extensively studies and are known. For example, the wavelength of about 254 nm has been determined to be optimal for killing common microorganisms found in water and air, and the wavelength of 293 nm is optimal for killing certain other types of microorganisms. These optimal wavelengths are in the UVB range (315 nm-280 nm) and UVC range (280 nm-100 nm). Such disinfection is typically combined with filtration to filter out larger organisms. The UV exposure to perform such disinfection is typically in the range of 2000-8000 uW s/cm2.
Currently, by far the most common UV emitters for disinfection are mercury-vapor lamps and xenon lamps. Such lamps emit a very wide range of UV wavelengths, and the vast majority of the emitted wavelengths (an associated power) have no effect on killing microorganisms. Such emitted wavelengths waste energy and can be harmful to humans over long exposure periods. Such lamps also need a high voltage power supply, which can create safety issues. The ideal UV emitter is one that generates a very narrow range of UV wavelengths, where the peak emitted wavelength is that which is the most efficient at killing the microorganisms of interest. UV LEDs approach such an ideal UV emitter since almost all optical power is in a very narrow band of wavelengths, and the peak wavelength can be controlled by the materials used in the active layer of the LED.
UV LEDs useful for disinfection are in their infancy, and commercially available UV LEDs that emit in the UVB and UVC wavelengths emit low power (e.g., less than 10 mW), are very inefficient, and are very expensive. The present assignee has developed much more powerful UV LEDs in this wavelength range, and a detailed fabrication process for forming such UV LEDs is described in U.S. patent application Ser. No. 14/635,903, filed Mar. 2, 2015, assigned to the present assignee and incorporated herein by reference.
It is inevitable that the costs of UV LEDs with a selectable and optimal peak emission within the UVB and UVC range will come down and the power levels per UV LED will greatly increase. Therefore, using such UV LEDs instead of relatively large mercury-vapor or xenon lamps will become much more cost-effective for disinfection.
Thus, novel designs for various disinfection systems using UVB and UVC LEDs are needed that make use of the added flexibility that small LEDs offer.